DESCRIPTION: (Scanned from the applicant?s abstract) The successful fusion of sperm and egg is the first and most critical step in an organism?s development. Understanding how and when fertilization successful takes place is critical to understanding population and species divergence, but the mechanisms of cell formation and division. The model organism with which to study gametic interactions is the free spawning sea urchin Echinometra, where sperm-egg recognition is the only barrier against undesirable or incompatible fertilizations. The protein that in part mediates the species-specific binding of sperm to the egg surface, bindin, is well characterized. The corresponding receptor of the egg surface however, has yet to be identified. I propose here an attempt to identify this and other female specific genes that are expressed only in the germ line tissues via RNA differential display. Female specific transcripts associated with the bindin gene (that is male specific are) perfect candidates for the unknown egg surface receptor. All female specific transcripts will be explored for their possible involvement in gametic interactions and ultimately species divergence.